Automatic level control for radio frequency amplifiers

Abstract

The disclosure relates to an automatic level control technique for RF amplifiers in a communication system, such as a wireless communication system. The invention provides an automatic level control technique to compensate for variations in the gain of an RF amplifier, which may be a transmitter amplifier or a receiver amplifier. In accordance with the invention, the gain of the RF amplifier can be controlled as a function of the output of a voltage controlled oscillator (VCO) circuit provided in the communication system. A VCO typically includes a buffer amplifier with a structure similar to that of the RF amplifier used in the transmit or receive side of the RF front-end. By tracking changes in the output of the VCO buffer amplifier, an automatic level control (ALC) input to the RF amplifier can be adjusted to compensate for process- and temperature-based variations in amplifier gain.

1. A device comprising:
 a voltage controlled oscillator (VCO) circuit; and 
 a first radio frequency (RF) amplifier with a gain controlled as a function of an output of the VCO circuit, wherein the VCO circuit comprises:
 a voltage controlled oscillator (VCO) that generates a VCO output; 
 a peak amplitude detector that detects a peak amplitude of the VCO output; 
 a comparator that compares the peak amplitude of the VCO output to a reference signal to control the VCO output; and 
 a second RF amplifier that amplifies the VCO output to generate the output of the VCO circuit. 
 
 
     
     
       2. The device of  claim 1 , further comprising a controller to activate the peak amplitude detector upon detecting a change in a frequency channel of a signal amplified by the first RF amplifier, and to deactivate the peak amplitude detector following the change in the frequency channel. 
     
     
       3. The device of  claim 1 , wherein the first and second RF amplifiers each include an inductive load. 
     
     
       4. The device of  claim 1 , wherein the peak amplitude detector is a first peak amplitude detector and the comparator is a first comparator, and further comprising:
 a second peak amplitude detector that detects a peak amplitude of the second RF amplifier; and 
 a second comparator that compares the peak amplitude of the second RF amplifier to a second reference voltage, wherein the second RF amplifier adjusts a control bias based on the comparison and generates an automatic level control (ALC) signal based on the control bias to control the gain of the first RF amplifier. 
 
     
     
       5. The device of  claim 1 , wherein the first RF amplifier controls the gain in response to the output of the VCO circuit by at least one of changing a tail current of the first RF amplifier, changing a transconductance of an input transistor of the RF amplifier, and changing an output impedance of the RF amplifier. 
     
     
       6. The device of  claim 1 , wherein the first RF amplifier controls the gain in response to the output of the VCO circuit by at least one of controlling parallel loads in the first RF amplifier, controlling a bias current source in the first RF amplifier, and adjusting at least one variable resistor in the first RF amplifier. 
     
     
       7. The device of  claim 1 , wherein the second RF amplifier comprises an analog to digital converter that generates a digital automatic level control (ALC) signal, and the first RF amplifier includes a digital controller that adjusts the gain of the first RF amplifier in response to the digital ALC signal. 
     
     
       8. The device of  claim 1 , wherein the VCO circuit is a phase locked loop (PILL) VCO circuit. 
     
     
       9. The device of  claim 1 , where the VCO circuit comprises a dedicated test circuit for the first RF amplifier. 
     
     
       10. The device of  claim 1 , wherein the device is a wireless communication device that communicates according to at least one of the IEEE 802.11 standards. 
     
     
       11. A method comprising:
 tracking a variation in an output of a voltage controlled oscillator (VCO) circuit, wherein tracking the variation includes detecting a peak amplitude of an output of a VCO of the VCO circuit, comparing the peak amplitude of the output of the VCO to a reference signal to control the output of the VCO, amplifying the output of the VCO, and detecting a peak amplitude of the amplified output of the VCO; and 
 controlling a gain of a radio frequency (RF) amplifier based on the variation. 
 
     
     
       12. The method of  claim 11 , wherein controlling the gain of the RF amplifier further comprises generating an automatic level control (ALC) signal based on the peak amplitude of the amplified output of the VCO. 
     
     
       13. The method of  claim 12 , further comprising generating a digital ALC signal. 
     
     
       14. The method of  claim 13 , wherein generating a digital ALC signal comprises generating a 4-bit digital word. 
     
     
       15. The method of  claim 11 , further comprising:
 activating a peak amplitude detector to detect the peak amplitude of the output of the VCO upon identifying a change in a frequency channel; and 
 deactivating the peak amplitude detector of the VCO output upon completion of the change in the frequency channel. 
 
     
     
       16. The method of  claim 11 , wherein the RF amplifier is a first RF amplifier, and further comprising:
 comparing the peak amplitude of the amplified output of the VCO to a second reference voltage; 
 adjusting a control bias of a second RF amplifier based on the comparison; and 
 generating an automatic level control (ALC) signal to control the gain of the first RF amplifier based on the control bias. 
 
     
     
       17. The method of  claim 11 , wherein controlling the gain of the RF amplifier further comprises generating an automatic level control (ALC) signal based on the peak amplitude of the amplified output of the VCO circuit, and controlling parallel loads in the RF amplifier based on the ALC signal. 
     
     
       18. The method of  claim 11 , wherein controlling the gain of the RF amplifier comprises adjusting at least one variable resistor of the RF amplifier based on the variation. 
     
     
       19. The method of  claim 11 , wherein controlling the gain of the RF amplifier comprises one of changing a tail current of the first RF amplifier, changing a transconductance of an input transistor of the RF amplifier, and changing an output impedance of the RF amplifier. 
     
     
       20. The method of  claim 11 , wherein the VCO circuit is a phase locked loop (PLL) VCO circuit. 
     
     
       21. A device comprising:
 means for generating a signal with a substantially constant amplitude; 
 a first amplifier that amplifies the signal; 
 means for generating an adjustment level control (ALC) signal based on the amplified signal; and 
 a second amplifier that controls a gain associated with the second amplifier based on the ALC signal. 
 
     
     
       22. The device of  claim 21 , wherein the means for generating a signal with a substantially constant amplitude comprises a voltage controlled oscillator (VCO) circuit. 
     
     
       23. The device of  claim 21 , wherein the means for generating the ALC signal comprises a peak amplitude detector that detects a peak amplitude of the output of the first amplifier and generates the ALC signal based on the peak amplitude. 
     
     
       24. The device of  claim 21 , wherein the second amplifier controls the gain in response to the ALC signal by one of changing a tail current of the second amplifier, changing a transconductance of an input transistor in the second amplifier, and changing an output impedance of the second amplifier. 
     
     
       25. The device of  claim 21 , further comprising:
 a peak amplitude detector that detects a peak amplitude of the generated signal with a substantially constant amplitude; and 
 a comparator that compares the peak amplitude of the generated signal to a reference signal to control the means for generating the signal. 
 
     
     
       26. The device of  claim 25 , further comprising a controller to activate the peak amplitude detector upon detecting a change in a frequency channel of the signal amplified by the first RF amplifier, and to deactivate the peak amplitude detector following the change in the frequency channel. 
     
     
       27. The device of  claim 21 , wherein the second amplifier controls the gain in response to the ALC signal by at least one of controlling parallel loads in the second amplifier, controlling a bias current source in the second amplifier, and adjusting at least one variable resistor in the second amplifier. 
     
     
       28. The device of  claim 21 , wherein the means for generating the ALC signal comprises an analog to digital converter and generates a digital ALC signal, and the second amplifier includes a digital controller that adjusts the gain of the second amplifier in response to the digital ALC signal. 
     
     
       29. The device of  claim 21 , wherein the first amplifier comprises a buffer amplifier, and the second amplifier comprises a radio frequency (RF) amplifier. 
     
     
       30. A device comprising:
 a voltage controlled oscillator (VCO) circuit that generates a signal with a substantially constant amplitude; 
 a first radio frequency (RF) amplifier that amplifies the signal generated by the VCO circuit; 
 a peak amplitude detector that detects a peak amplitude of the amplified signal from the first RF amplifier and generates an adjustment level control (ALC) signal based on the peak amplitude; and 
 a second RF amplifier that controls a gain associated with the second RF amplifier based on the ALC signal generated by the peak amplitude detector. 
 
     
     
       31. A method comprising:
 generating a signal with a substantially constant amplitude with a voltage controlled oscillator (VCO) circuit; 
 amplifying the signal generated by the VCO circuit with a first radio frequency (RF) amplifier; 
 detecting a peak amplitude of the amplified signal received from the first RF amplifier; 
 generating an adjustment level control (ALC) signal based on the peak amplitude; and 
 controlling a gain of a second RF amplifier based the ALC signal generated by the peak amplitude detector. 
 
     
     
       32. A method comprising:
 generating a signal with a substantially constant amplitude; 
 passing the constant amplitude signal through a first amplifier; 
 tracking variations in the first amplifier output; 
 generating an adjustment level control (ALC) signal based on the variations in the first amplifier output; and 
 controlling a gain of a second amplifier as a function of the ALC signal. 
 
     
     
       33. The method of  claim 32 , wherein tracking variations comprises:
 detecting a peak amplitude of an output of the first amplifier; and 
 comparing the peak amplitude to a reference signal to control the output of the first amplifier. 
 
     
     
       34. The method of  claim 32 , wherein generating a signal with a substantially constant amplitude comprises generating a signal with a phase locked loop (PLL) voltage controlled oscillator (VCO) circuit. 
     
     
       35. The method of  claim 32 , wherein generating a signal with a substantially constant amplitude comprises:
 detecting a peak amplitude of an output of a voltage control oscillator (VCO); and 
 comparing the peak amplitude of the output of the VCO to a reference signal to (control the output of the VCO. 
 
     
     
       36. The method of  claim 32 , wherein the first amplifier comprises a buffer amplifier, and the second amplifier comprises a radio frequency (RF) amplifier.